Solvent extraction with liquid carbon dioxide



March 17, 1953 Filed May 8, 1950 A. W. FRANCIS SOLVENT EXTRACTION WITH LIQUID CARBON DIOXIDE y 9 Sheets-Sheet l March 17, 1953 A. w. FRANCIS 2,631,966

SOLVENT EXTRACTION WITH LIQUID CARBON DIOXIDE Filed May 8, 1950 9 Sheets-Sheet 2 fm/l0 ('02 @MLB @gg/M March 17, 1953 l A. w. FRANCIS 1 2,631,966

soLvENT ExTRAcTIoN WITH LIQUID CARBON 1110x105:

Filed Mays, 195o 9 sheets-sheet s YL/au//D @02 fai/f March 17, 1953 4A. w. FRANCIS 2,631,966

SOLVENT EXTRACTION WITH LIQUID CARBON DIOXIDE Wb. fggww March 17, 1953 A. w. FRANCIS 2,531,966

SOLVENT EXTRACTION WITHLIQUID CARBON DIOXIDE March 17, 1953 A. w. FRANCIS 2,631,955-

SOLVENT EXTRACTION WITH LIQUID CARBON DIOXIDE Filed May e, 1950 9 sheets-sheet e 7^ I Z@ mu/ '02 L/Il//D '02 I WD. W

March 17,l 1953 A. w. FRANCIS 2,531,966

soLvE-NT ExTRAcTIoN WITH LIQUID CARBON DIOXIDE:

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March 17, 1953 A. w. FRANCIS 2,631,955

SOLVENT EXTRACTION WITH LIQUID CARBON DIOXIDE Filed May 8, 1950 9 Sheets-Sheet 8 March 17, 1953 A. w. FRANCIS 2,631,965

SOLVENT EXTRACTION WITH LIQUID CARBON DIXIDE Patented Mar. 17, 1953 UNITED STATES PATENT OFFICE 19 Claims.

This invention has to do with extraction with certain selective solvents of various mixtures, and particularly hydrocarbon mixtures such as 1ubricating oil stocks', Yto Vseparate the mixtures into fractions having different properties.

Numerous processes have been developed for the separation of hydrocarbons and hydrocarbon derivatives of different molecular configuration by taking advantage of their selective solubility in selected reagents or solvents from which they later can be separated. Exemplary of hydrocarbon separation procedures is the Edeleanu process, wherein paraiiinic materials are separated from aromatics by virtue of the greater solubility of aromatics in liquid sulfur dioxide. Lubricating oil solvent reiining processes, solvent deasphalting, solvent dewaxing and the like are further examples of the separation of hydrocarbons of diierent molecular configuration.

Many liquids have been proposed and some of them have been used as selective solvents for effecting separation of different classes of hydrocarbons. They vary greatly in selectivity and in applicability for various boiling ranges of hydrocarbons. For the same boiling range the solubility increases in the order, paraffins, naphthenes, olens, alkyl benzenes and polycyclic aromatics for practically all available solvents. For many extractions this is a convenient order, since small quantities of polycyclics which are detrimental to the viscosity index of a lubricant, can be removed by suitable solvents. In other cases, a reverse order of selectivity would be more convenient. Solvents having the latter selectivity are probably so characterized only when used in the vicinity of their critical temperatures. For example propanecritical temperature, 95.6 C.- has been used at 80-100 C. for solvent refining of vegetable oils, but for mineral oils it has a very limited applicability, because only a few polycyclics separate at all and the selectivity is slight. Ethane-critical temperature, 32.3 C.is no better in this respect.

Liquid carbon dioxide, however, has unusual miscibility relations with hydrocarbons and other substances, for it dissolves aliphatic and monocyclic aromatic hydrocarbons in preference to polycyclics of the same boiling range. The selectivity is many times greater than that manifested by propane and ethane. The miscibility relationship, then, is the reverse of that with almost all other solvents in which the more highly cyclicized hydrocarbons are more soluble. While liquid carbon dioxide is advantageous in view of this unusual miscibility characteristic, and is also favored by low cost, non-corrosiveness, nontoxicity, and ease of recovery from extract and raflinate phases, its use is limited by its complete miscibility with most gasoline hydrocarbons, and on the other hand by its slight solubility for lubricating oils. For example, it has been shown that the maximum solubility for a typical lubricating oil in liquid carbon dioxide is only 0.9 per cent at C.; and at 25 C., the solubility is only 0.72 per cent. To one skilled in the art, it is obvious that these solubilities are too low for practical purposes.

Carbon dioxide has a critical temperature of 31.1 C. (88 F.).

This invention is predicated upon the discovery of an advantageous and practical solvent extraction procedure in which liquid carbon dioxide is used in combination with certain solvents with which it cooperates.

PRIOR ART One of the rst to extract oils with liquid carbon dioxide was Auerbach. As shown by Auerbach in U. S. Letters Patent 1,805,751 and related foreign patents (Canadian 285,782, and British 277,946 and 285,064), certain light lubricating oil fractions are soluble in liquid carbon dioxide to the extent of only about three per cent. Schilling and Stadler (2,029,120) also described a selective separation with liquid carbon dioxide, showing the removal of unsaturated hydrocarbons from gas mixtures.

Several investigators have also described a selective separation of hydrocarbons in which liquid carbon dioxide is used in combination with liquid SO2 (2,034,495; 2,346,639; German 546,123). Refining of petroleum fractions to eiect removal of sulfur compounds, using S03 in combination with liquid carbon dioxide is disclosed by Gary (1,893,138).

Low molecular weight parains, such as propane, have also been used with liquid carbon dioxide in extracting hydrocarbon mixtures. This is shown by Lantz (2,188,051).

Liquid carbon dioxide has also been described as a selective extractant by Webb (2,246,227). Typical of the diluents shown by the latter for use with liquid carbon dioxide are: hydrocarbons su-ch as propane; solvents such as acetone, pyridine, liquid SO2, cresylic acid and other solvents of the type of preferential solvents for nonparafiinic hydrocarbons. A similar disclosure is found in 2,281,865 (van Dijck) used with liquid carbon dioxide are hydrocarbons and solvents known as selective or naphthenic (or aromatic) solvents such as furfural, nitrobenzene, Chlorex, cresylic acid, phenol, aniline and quinoline. The solvents used by van Dijck are necessarily employed in relatively small quantities, actually only those quantities which are miscible with an oil. In the cases of furfural, aniline and phenol, the quantities used are minuteof the order of one or two per cent. Pilat and Godlewicz (2,315,- 131) have modied the processes described by Lantz, Webb, and van Dijck, by using gaseous carbon dioxide with another solvent such as a hydrocarbon or a selective or naphthenic solvent.

of fractions of diierent properties are obtained by contacting -a mixture of compounds, particularly lubricating oil stocks, with liquid carbon ally, these solvents B do not form solid salts with carbon dioxide at temperatures of 20 C. and higher. Still another characterizing feature of this family of solvents is their failure to form three individual phases with liquid carbon dioxide and the mixture to be resolved. Again, for ease of operation, the solvents B should have melting points not greater than about 60 C. Representative solvents B having such properties include: aniline, o-chloroaniline, m-chloroaniline, cresols (o, and p), o-toluidine, tetrahydrofurfuryl alcohol, phenylethanol, pinacol, phenol phenylacetonitrile, hydrocinnamaldehyde, methyl phthalate, o-nitrochlorobenzene, betahydroxyethyl acetate, o-nitrobiphenyl, o-anisidine, benzcic anhydride, cinnamaldehyd-e, triethylene glycol, benzyl alcohol, and ethyl phthalate. Of these solvents, tetra'hydrofurfuryl alcohol has proven particularly advantageous. Aniline has also been highly effective when used in the treatment of a naphtheni-c type oil stock.

Triethylene glycol and ,li-hydroxyethyl acetate (included in group B) form` three layers with liquid carbon dioxide and certain mixtures, such as lubricating oils. Yet, they do not form three layers when used with liquid carbon dioxide and methyl naphthalenes.

The hydrocarbon miscibilities of solvents A and B, together with carbon dioxide solubilities for solvents of type B, are shown in Table I, below.

Table I maar S lvent carbon o Miscibhty for ooi in co2 A Cellosolve a Ethyl chloroacetatc. a Isonropyl alcohola l -Nitrcpropane a Carbit a Benzonitr a Chlorex a Diacetone alcohol. a Ethyl lact a Ethyl oxalate a Ethyl acetoacetate.. b Ethyl succinate b o-Cresol (M. Pt. 30 C.) a 30 2 p-Cresol (M. Ft. 36 0.). a 30 2 N-methyl aniline a 40 2O o-Toluidine a 37 7 a 25 5 a 55 17 b 27 8 b 60 l0 b 42 2l b 3 b l5 3 c 3 o-Anisidinc c 20 l Benzoic anhydride (M. Pt. 42 C.) c 20 3 Cinnamaldehyde c 20 4 Methyl phthalate c 43 6 o-Nitrobiphenyl (M. lt 37 C c 15 2 Phenylacetcnitrile c 52 13 Pinacol (M. Pt. 38 C.) c 23 2 Tetrahydrofurfuryl alcohol c 20 3 m-Chloroaniline c 23 1 B-Hydroxyethyl acetate. d 50 17 Triethylene glycol d 12 6 Ethylene glycol e 7 0.2

lHydrccarhon miscibilitics at 25 C. as liquid. A solid is considered miscible with a hydrocarbon or carbon dioxide if it is highly soluble in it (e. g., over 40%) without the formation of liquid layers in equilibrium. If a substance is miscible with one group ol hydrocarbons, as indicated by a footnote letter, it is also miscible with all of the hydrocarbons indicated by letters following this one in the series. Thus, "a" means a, b, c, d, b actually means 'D, c, d; "c means 0, d.

2 Solubilitics oi' 2% or less are approximations (i170), in view of thc difficulty in determining the same.

a-Miscible with n-heptane.

b-Miscible with mcthylcycloh exane and lower naphthenes.

c-Misciblc with (ii-sec-butyl) benzene and lower aromatics.

d-Miscible with benezene.

e-Not miscible with any hydrocarbon.

The foregoing solvents and liquid carbon dioxide are effective in resolving various mixtures into a multiplicity of fractions, or compounds, of different properties. They are particularly advantageous in the resolution of lubricating oil stocks, representative of which are Pennsylvania, Mid-Continent and Coastal types, or parainic, naphthenic and aromatic types. Other hydrocarbon mixtures successfully treated include gas oils, fuel oils, shale oils, transformer oils, cable oils, coal tar fractions, etc. Still other mixtures which can be treated with appropriate solvents of groups A and B, include: mixtures of alcohols, such as those obtained by hydrogenation of oxides of car-bon; mixtures of vegetable oils; mixtures of aromatic amines; etc.

In order that this invention may be more readily understood, typical separations are described below with reference being made to the drawings attached hereto.

In Figure I, a charge such as a highly naphthenic lubricating oil stock, for example, one having a `density of 0.910, a refractive index (nDZU) of 1.5076 and a critical solution temperature (aniline) of 72 C., in tank l is introduced through line 2 to extractor 3. Chlorex in tank 4, is introduced through line 5 into an upper section of 3, and liquid 4carbon dioxide in tank S is introduced through line l to a lower section of 3 wherein each solvent flows countercurrent to portions of the oil charge. It will be understood that the extractor 3 can comprise conventional countercurrent stage or tower extraction equipment. Contact of Chlorex, liquid carbon dioxide and oil can also be aided by conventional packing material in extractor 3.

The temperature of the oil and solvents in extractor 3 should be not much greater than about 31.1 C., the critical temperature of carbon dioxide. Slightly higher temperatures, up to about 36 C., can be used in some cases because enough solvent (A or B) and/or hydrocarbon may dissolve in the carbon 4dioxide-rich phase to make it liouid alcove the critical temperature of pure carbon dioxide. This temperature condition can be realived by maintaining .both the oil and solvents at the required temperature prior to introduction to the extractor 3. or the latter can be maintained at the reouired temperature by well known cooling or heat exchange means. The pressure in extractor 3 is maintained suilcientlv high so as to maintain a phase rich in carbon dioxide in the licuid state.

The ratio of solvent, Chlorex to oil in the extractor 3 is preferably maintained within the range of 1:1 to 2:1. and that of liouid carbon dioxide to oil within the range of 1:1 to 5:1. This feature is explained in more detail hereinafter with reference to a phase diagram Ifor the system liquid carbon dioxide-Chlorex-lubricating oil.

In the extractor 3, a raffinate nba-se and an extract phase are formed. The rainate phase (the heavier phase) contains a relatively large proportion of the nolycyclic hydrocarbons present in the oil charge and some pavaflins and nanhtbenes. Also present in the ranate phase is Chlorex and carbon dioxide. The rafnate phase is withdrawn from extractor 3 through line 3 to solvent recovery vessel 9. The raffinate is fractionated in 9, with the Chlorex and carbon dioxide being taken overhead through line l0 and recycled through line 5. This fractionation can be accomplished by using high temperature, or it can be accomplished by countercurrent extraction :with liquid. carbon dioxide :as :described in..copendingfapplication .Serial :No.162,587,'led May 8,1950. A rannate -oil fraction is removed from Sthrough Il this fractionisfsuitable .for use,' for example, asaninsecticidal oil.

'The `extract phase in extractor 3 .isremoved .through line l2 to vessel I3, which isequipped lwith suitable means lforeiiecting lrelease of carbondioxide from the-extract phase. For example, a heat exchange vmedium :can .be vcircula-ted through the Wall of vvessel H3 or through coils therein, to raise the temperature of `the'extract phase. Also, pressure-reducing means can be provided. In vessel I3, then, carbon dioxide is removed through-line i4 and'recycled to `reservoir 5. in line lll, a-condenser (not shown) is used whencarbon dioxide'is removedby applying heat to vessel'fl; ora 'compressor (not shown) is :positioned in .line l vwhen carbon dioxide is removed by pressurel reduction. The extract fphase, Vsubstantially ,free 'of carbon'dioxide, isitairen through'line |'5 tosettler i6. When the -extract phase is allowed toistand in settler` I6, ra .further separation takes place, with"the formation of an vrextract-'extract phase vand an extract-raiiinate; phase. "Ihusg a double extractionV is effected-upon removalof the carbon dioxide. The extract-raffinate contains the high quality lubricating components ofthe charge and some Chlorex. rIhis is takenthroughline Hand fractionatedin 'solvent recovery vessel 'l 0. Again, the fractionation can ibe accomplished `by -distillation or by countercurrent extraction fvvith liquid .carbon dioxide. -Chlorex and 'residual carbon dioxide -(if used) are taken overhead through line i9 and recycled to :fline l0 and reservoiri. The high quality oilis removedfrom I-B-as a bottom `product.through-line 20. 'Ihe oil removed through line .20 Ahas -a substantially higher viscosity index thanfthe :original charge and other fractions thereof.

Theextr-act-extract"separated insettler I6 is taken through line :2| and -distilled -in VVstill-.22. Chlorex and anyI resi-dual Icarbondioxide present in the extract-extract 'are removed overhead throughline 23 andfreoycled' through linel. An extract-extract oil fraction, substantially rfreeof Chlorex 'and carbon dioxide, `.is removed `from still 22 through line 24, It Willbe-understood that the -extract-extract .fraction (line .-2I) and/or the-rstraiiinate (linaS) can be y recycled to the extractor -3 if desired, and `if fsm-.the Chlorex and carbon dioxide-present'therein need not be=removed `before-therecycling operation.

A representative .procedure inwhich a solvent of type B, above, is'used'isshown by Figure 2. .In this procedure, tetrahydrofurfuryl alcohol .is .the solventi'cooperatingavith,liquid carbon dioxide to provide a multiplicity of fractionshavingdifferent properties. A charge such. as ,the -lubricating oil stock described in connection with Figure 1, above, is A.taken from reservoir..,30, through line 3l, to-ex-tractor 32. Tetrahydrofurfuryl alcohol intank-33,is,.taken through line llintoan upper section of 32, .and liquid carbon .dioxide `in tank 35 is taken through line .36. and `introduced finto a lower section of extractorZ. Thematerials inextractor Y.t 2` are maintained ,under pressure. and at a suitable temperature as discussed earlier in connection with extractor 3. Here too, a rafnate phase and an extract phase are formed. The railnate phase (the heavier phase) contains a preponderance of the polycyclic hydrocarbons present inthe Ioil charge, in association with some tetrahydrofurfuryl alcohol and-carbon dioxide. "The `ra'linate phase, vstill .under pressure.

is brought from extractor 32 through line 3.1 to carbon dioxide recovery vessel 38. The latter `is equipped with suitable pressure'reducing and/or temperature increasing means in order that carbon dioxide can be separated. Upon removal of carbon dioxide through line 39, the raflinate is taken through linell to settler 4 I. The raiiinate in settler 4l, separates upon standing, thus providing a rainate-rainate phase (upper layer) and ra raflinate-extract phase. The rainnateraffinate lcomprises an oil of intermediate quality and some tetrahydrofuriuryl alcohol. The railinate-'rai'linate can be taken through line i2 and recycled to reservoir 30, as shown; Vor it can be distilled (not shown),if desired. The tetrahydrofurfuryl alcohol and oil recovered upon distillationpanbe recycled separately. The ramnate-extract `phase separated in settler il is removed from the system via line A3. rlhe latter phase comprises alow quality oil fraction, rich in polycyclic components vof the oil charge, and tetrahydrofurfuryl alcohol. It will be understood that this phase can be distilled to recover the tetrahydrofuriuryl alcohol, andthe latter can be recycled toreservoir 33, although the recycling is notshoWnin-Figure 2. Also, while the oil fraction recovered through line 153 is a relativelypoor lubricant, it has value, for example, as an insecticidal-solvent oil for DDT (2,2-dichlorodiphenyltrichloroethane) The extract phase which separates in extractor 32, is removed through line 44 to carbon dioxide recovery vessel 45. The latter is of the same character as vessel 33, such that carbon dioxide is removed overhead through line 46 and recycled to `line 39. Upon removal of carbon dioxide from the extract phase, the latter is taken through line 4l to settler 48. Here too', a, further separation occurs; with carbon dioxide removed, an

extract-rainate phase and an extract-extract phase areformed. The extract-ra'inate phase (upper layer) contains high quality oil and some tetrahydrofurfuryl alcohol and residual carbon dioxide, and is taken through line 49 to solvent recovery vessel 50. Tetrahydrofurfuryl alcohol and .residual carbon dioxide are fractionated overhead from 50 and are recycled through line 5l high quality lubricating oil is removed as a bottoms product through line 52.

'The extract-extract phase in settler d@ is removed through line 53 and recycled to line 152 and reservoir 30. Inasmuch as this phase contains some tetrahydrofurfuryl alcohol and residual carbon dioxide, the phase can be distilled (not shown) and the individual products-oil, tetrahydrofurfuryl alcohol and carbon dioxidecan be recycled separately, if desired.

It will be recognized that the Aforegoing illustrations provided by Figures `1 and 2 are diagrammatic, and that pumps, heaters, coolers, heat exchangers, pressure vessels of various character can be employed.

As indicated above, carbon dioxide-is used inv liquid form, thus requiring the use of relatively low temperature and high pressures. In effect,

the operatingtemperatures will be not more than slightly-above the critical temperature of carbon dioxide, namely, 31.1 C., and preferably below it. While the temperature can be lowered considerably below 31.1 C. satisfactory operation has been realized with temperatures withinthe range of 10 C.to'f35 C. Operating pressures are relatively high, generally about 1000 pounds per squareinch (or '70 atmospheres). Usually, pressures are ofthe order of 600 to 1200 pounds per square inch, dependingupon, the temperatures employed. Higher pressures make it possible to sure of 1000 pounds per square inch (p. s. i.) and a temperature of 24 C., the solubility of n-octadecane in liquid carbon dioxide was found to be about three per cent; whereas, with a pressure of 4000 pounds per square inch and a temperature of 24 C., the solubility was eleven per cent. This phenomenon of increased solubility due to contracting on mixing is advantageous, particularly inasmuch as the solubility of lubricating oils in carbon dioxide is undesirably low at the vapor pressure of carbon dioxide. The increase from 3% to 11%, mentioned above, is unusual since the density of the solution is increased enough to make the undissolved oil float upon the solution. The pressure at which the inversion occurs varies with the density of the oil, being high for oils of high density and vice versa. With a decrease of pressure, as by opening a pressure reducing valve, a small amount of oil is released, whereupon the layers are inverted again. This increases the volume of undissolved oil. In this way, liquid pressure can be used to control the solubility of the oil.

The invention is further illustrated by experimental data obtained with liquid carbon dioxide and solvents of types A and B. These experimental data are presented in the form of charts, or more particularly ternary diagrams, identified here as Figures 3 to 50. These diagrams can be used to determine: the suitability of a solvent for a desired separation; the approximate selectivity of the solvents; the range of compositions of liquid carbon dioxide, solvent A or B, and the mixture to be treated; the approximate number of stages or extractions necessary to eiect a separation of desired degree; etc.

Figure 3 represents the system liquid carbon dioxide, Chlorex (,dichlorcdiethyl ether) and lubricating oil. It is to be understood that in Figure 3 and in all of the ternary diagrams involving lubricating oil, the phase boundaries are necessarily approximate since the oil is not a pure substance. In fact, the purpose of the fractionations is to separate it into fractions of different properties, which include miscibilities with the solvents. Therefore, with countercurrent operation in extractor 3 of Figure 1, for example, the effective diagram of Figure 3 is appreciably different at the bottom and at the top of the extractor. At the top of the extractor, curve CD of Figure 3 is higher and broader, and curve AERB is shallower. At the bottom of extractor 3, the reverse change appears.

The oil is a highly naphthenic distillate stock having the following properties:

A. P. I. gravity 23.80 Density 0.910 Refractive index, 11.1320 1.5076 Critical solution temperature (with aniline), C 72 Pour point, F 20 Flash (open cup), F 395 Fire, F 455 Viscosity, centistokes at 100 F 28.65 Viscosity, centi'stokes at 210 F 4.51 Viscosity index 60 Viscosity gravity constant 0.871 Color, Lovibond 18 Figure 3 reveals that Chlorex and liquid carbon dioxide are completely miscible, and that Chlorex and the oil are incompletely miscible. Mixtures falling within the area defined by curve AERB separate into two layers. One of the layers which separates contains a larger amount of oil in proportion to carbon dioxide, and the other a larger amount of carbon dioxide in proportion to oil. The proportion of these two phases, as well as the concentration thereof, can be determined by the tie lines extending between the sides of the binodal curve across the area of immiscibility. For example, a mixture of 20 per cent Chlorex, 60 per cent carbon dioxide and 20 per cent oil, represented by point S, comes within the area of immiscibility and separates into two phases. The composition of the two phases is determined by the extremities of a tie line E-R passing through the point S. The composition ofY the extract phase, E, is about 21 per cent Chlorex, about 70 per cent carbon dioxide and about 9 per cent oil. The rafnate phase, R, contains about 17 per cent Chlorex, about 30 per cent carbon dioxide and about 53 per cent oil. The proportion of extract layer to raflinate layer by weight is determined by the ratio of line SR to line SE, and the actual quantities of each can be calculated from the known charges and compositions of the extract and raffinate layers.

Figure 3 also shows that as carbon dioxide is removed from the extract phase, E, following line AEF, two additional layers are formed. Thus, mixtures coming within the area dened by curve C-D separate into two layers, namely an extract-extract phase, C, and an extract-rafnate phase, D. The extract-extract phase, C, contains about 92 per cent Chlorex and about 8 per cent oil; the extract-raffinate phase, D, contains about 42 per cent Chlorex and about 58 per cent Oil. The oil in the extract-raffinate phase, isolated by removing the Chlorex, is of excellent quality. In contrast, the oil present in the extract-extract phase is of intermediate quality and can be recycled with the Chlorex associated therewith or following isolation from the Chlorex.

When carbon dioxide is removed from the rafnate phase, R, a Chlorex-oil raiinate is obtained. The latter contains about 24 per cent Chlorex and about 76 per cent oil. This oil fraction is of low quality as a lubricant, having less lubricant value than the oil charge.

Properties of the oil products, after removal of both solvents, are as follows:

- Aniline Refractive Index, 11h20 Poomt on Chart-e 1.5016 72 Rafnate (from R) 1.5228 35 Extract-extract (from C) 1. 5025 73 Extract-rainate (from D) 1. 4790 89 Figure 8: liquid carbon dioxide-ethyl lactatelubricating oil. Y

In Figures 4 through 8, for the lower curve, the oil-rich phase is the lighter and ltherefore upper layer, except with isopropanol (Fig. 4). For the upper curve, the oil-rich phase is the heavier, except in Fig. 6, below the dotted line, which is an isopycnic. The latter is a tie line connecting compositions of phases of equal density. Between this line and the curve, the oil-rich phase is the lighter one.

When benzonitrile is used with a heavy oil stock and liquid carbon dioxide, the ternary diagram which represents the system is quite similar to Figure 3, above.

In contrast to Figures 3 through 8, systems are shown in Figures 9, and 11 in which the two curves are merged. In these, asin Figures 3-8, liquid carbon dioxide is miscible with the solvent, but neither is miscible with the hydrocarbon component. Figure 9 shows liquid carbon dioxide-acetone-lubricating oil; Figure 10: liquid carbon dioxide-acetonitrile-lubricating oil; and Figure 11: liquid carbon dioxide-ethyl alcohollubricating oil. Thir-ty-ve other such systems have been studied.

Figure 12 shows the ternary system, liquid carbon dioxide-aniline-lubricating oil. The oil used is the same as in Figure 3. As revealed by Figure 12, aniline is incompletely miscible with the oil and also incompletely miscible with liquid carbon dioxide. Three binodal curves are formed, and of these two merge. The curves defining the areas in which mixtures separate into two layers are F--VV--GV (solid line), H-I-V-L and K-I-V-J. By way of illustration, a mixture of i9 per cent aniline, 11 per cent liquid carbon dioxide and 40 per cent oil, represented by the symbol M, is within the area of immiscibility, and separates into two layers. The -composition of the extract phase, X, is about 78 per cent aniline, about 12 per cent carbon dioxide and about 10 per cent oil; the raffinate phase, Y., contains about 18 per cent aniline, about 10 per cent carbon dioxide and about '72 per cent oil. This is essentially an extraction of oil with aniline, with the raiinate Y of higher quality as a result of the selectivity of aniline. The solubility of oil in aniline is augmented greatly yby the presence of carbon dioxide, thus permitting a much smaller volume of solvent (aniline) and a larger capacity for oil to be treated.

An extraction between V and I is essentially a liquid carbon dioxide extraction, the quality of the oil in V being better than in I. Thecooperation between aniline and liquid carbon .dioxide is evidenced by the greater vsolubility of the'oil at V than at J, that is, without aniline.

With aniline, and other solvents of type vB in combination with liquid carbon dioxide, the extract phase V separates into two additional layers when carbon dioxide is removed therefrom. Since the extract phase V is of higher quality, that is, more parailinic than the original oil, its mutual miscibility with aniline, after reducing its carbon dioxide content, is less, requiring a larger curve, dotted line e r'. As shown in Figure 12, an extract-extract phase, e', is obtained, together with an extract-raflinate phase, 1". The extract-extract phase contains an oil of intermediate quality; this is generally recycled with the aniline associated therewith or recycled alone following separation from aniline vby distillation or other suitable procedure. The extract-rafnate phase contains about 10 percent aniline Figure 22:

vand about 90 per cent of oil. The latteroil is lof excellent quality and `is withdrawn from-the system. l

Surprisingly, the raffinate` phase, I, also separates into two additional layers when ycarbon dioxide is'removed therefrom. A lower curve, e r defines this separation, since this oil is more naphthenic and is more miscible with aniline, with the raiinate-rafnate as The raffinate-extract comprises about 92 per cent aniline vand about 8 per cent oil, the oil being of poor quality. The latter is separated from aniline by distillation, by'extraction with liquid carbon dioxide, or by washing vwith acid, etc., and is removed from the system. The ranate-rafnate, r, contains about 20 percent Yaniline and about per cent oil of intermediate quality. The latter oil is recycled, and need not be separated from the aniline admixed therewith.

FiguresY 13 through 32, inclusive, are ternary diagrams for systems similar to that shown vin Figure 12, that is, wherein aniline is replaced with other solvents of `type B. In Figures 13 through 32, inclusive, liquid carbon dioxide and the naphthenic oil,A described above, are used with the following solvents, unless-otherwise indicated:

tetrahydrofurfuryl alcohol, or o-anisiphenol o-ni-trobiphenyl methyl phthalate phenylacetonitrile Figure 18: hydrocinnamaldehyde Figure 19: o-nitrochlorobenzene Figure 20: pinacol Figure 21: phenylethanol cinnamaldehyde o-toluidine oor p-cresol, with n-hexadecane Figure 25: -hydroxyethyl acetate, with :tetralin Figure 26: hydroxyethylacetate, with a-methylnaphthalene Figure l27: tetrabromoethane with n-tetradecane Figure 28: triethylene glycol, with a-methylnaphthalene Figure 29: 'N-methyl aniline,

(a highly refined paraffin oil) Figure 30: ethylene glycol, with n-decyl alcohol Figure 3l: o-chloroaniline, with n-hexadecane Figure 32: m-cresol, withn-hexadecane Eachsystem can Vbeusedffor a double-or multiple-extraction of oil as inthe examplestdescribe'd. Some of the solventsm'entioned are :solidsat 25 C., namely,V phenol, :"o-nitrobiphenyl, o-nitrochlorobenzene, pinacol, oandp-cresol as `indicated by a lineacross the solvent corner, but each of these solvents .except phenol vdissolves enough carbon dioxide -toliquefy it at room temperature. Phenol'is liqueed by the presence of bothrcarbon dioxide-and lubricating oil.

In contrast with the foregoing results obtained with liquid carbon dioxide in combination with a solvent of type A or B, 'results of aquite diierent character'have been obtained with other. wellknown solvents in combination with liquid carbon dioxide. For example,rFigure 33 shows the type of ternary diagram obtained with any mutually miscible pair of liquids, each of whichis miscible with liquid carbon dioxide; typical of such a system is: liquid carbon dioxide-methyl alcohol-benzene. Innumerable systems of this Figure 23: Figure 24:

with crystal oil 13 character can be found. It is obvious that extraction is possible with such a system.

Figures 34 and 35 show systems in which liquid carbon dioxide is miscible with the solvent and the third component, a hydrocarbon, but the solvent and hydrocarbon are incompletely miscible with each other. The systems are: liquid carbon dioxide-sulfur dioxide-kerosene (boiling range, 150 to 30()Q C.) and liquid carbon dioxide-methanol-kerosene. Eleven such systems have been studied. A more complicated relationship is that obtained with liquid carbon dioxide-formic acid-n-tetradecane, wherein three liquid phases are formed; this is shown by Figure 36. Thesystem represented in Figure 37 is further complicated by a solid phase and two liquid phases; this is liquid carbon dioxide-chloroacetic acid-n-heptane.

When liquid carbon dioxide and the solvent used are not miscible, but each is miscible with the hydrocarbon component, the ternary diagram is of the character shown by Figure 38. The system, liquid carbon dioxide-m-cresolkerosene (B. R. 150 to 300 C.) is shown by Figure 38. More than iifty such systems have been studied; but, as will be apparent, these systems are unlike the systems coming within the present invention.

Systems in which the solvent serves as a diluent for the hydrocarbon component so as to increase the solvent power of liquid carbon dioxide for the hydrocarbon, are illustrated by Figures 39-41. In other words, these systems involve a solvent miscible with the hydrocarbon and with liquid carbon dioxide, but the hydrocarbon and liquid carbon dioxide are incompletely miscible. Figure 39 shows liquid carbon dioxide-propanelubricating oil (same as in Figure 3) Figure 40, liquid carbon dioxide-nitrobenzene-lubricating oil (same as in Figure 3) Figure 41, liquid carbon dioxide-thiophene (also pyridine) lubricating oil (same as in Figure 3). More than ninety such systems have been studied; however, they stand apart from the present invention.

Another type of system is that wherein liquid carbon dioxide is miscible with a hydrocarbon component, and wherein neither liquid carbon dioxide or the hydrocarbon is miscible with the solvent. Representative of this type of system is liquid carbon dioxide-phenol-n-heptane, shown by Figure 42. More than sixty such systems have been studied but, here again, they are not pertinent to the present process.

An unusual relationship is shown in Figure 43 by the system liquid carbon dioxide-formic acidn-hexadecane, wherein three liquid phases are formed although two of the components are mutually miscible. The unusual feature is due probably to the unique property of formic acid in being miscible with anhydrous carbon dioxide, although practically immiscible with every hydrocarbon.

When the solvent and hydrocarbon are miscible, but neither mixes completely with liquid carbon dioxide, a ternary diagram of the type illustrated by Figure 44 is obtained. The system in the latter figure is liquid carbon dioxide-mcresol-lubricating oil. More than fifty other sys tems of this class have been studied.

In the event that no pair of the three components is completely miscible, three binodal curves characterize the ternary diagram. These curves can be separate as illustrated by Figures 45, 46, 47 and eighteen other related systems which have been studied. Other combinations giving three separate curves are those of liquid carbon dioxide and decalin and either a-chloropropionic acid, aldol, -chloroethanol, furfuryl alcohol or dipropylene glycol; those of liquid carbon dioxide and n-tetradecane with hydrocinnamaldehyde, pchlorophenol, benzyl alcohol or m-cresol; those of liquid carbon dioxide and n-hexadecane with eugenol, benzal acetone, hydrocinnamaldehyde, oor p-toluidine, tetrahydrofurfuryl alcohol, or o-nitrochlorobenzene; and liquid carbon dioxide and l-octadecene with m-toluidine. Two of the three curves can be merged as in Figures 9-32, or as in Figure 48. The latter type is exemplified also by systems of liquid carbon dioxide and betahydroxyethyl acetate with decalin or n-tetradecane.

Finally, all three binodal curves can be merged, providing three layers of compositions represented by the corners of the inside triangles of Figures 49 and 50. This type includes also the systems of liquid carbon dioxide and lubricating oil with furfuryl alcohol or cinnamyl alcohol; those of liquid carbon dioxide and n-tetradecane with propylene glycol, triethylene glycol or ethylene glycol; liquid carbon dioxide-decalin-triethylene glycol; liquid carbon dioxide-transformer oilaniline liquid carbon dioxide-tetralin-triethylene glycol; liquid carbon dioxide and a-methylnaphthalene with formamide or diethylene glycol.

The data from which Figures 3-50 were prepared, were obtained with a visual autoclave, operating at room temperature, about 25 C. The autoclave is a Jerguson gauge of 116 parts by volume capacity, with thick narrow Pyrex glass windows front and back. Incandescent lamps are mounted behind the vertical position of the autoclave. Agitation of the materials is obtained by rotation of the autoclave, end-ove'r-end, within a heat-insulated case. The latter is provided with strip heaters which permit heating by radiation, and with means for cooling to low temperature. The autoclave was charged with the liquid reagents, the carbon dioxide being introduced from a cylinder. Solubility of carbon dioxide in another liquid was estimated by charging a denite volume of that liquid and then adding carbon dioxide until after agitation a new liquid phase appeared (at the top). Then additional increments of liquid carbon dioxide were added. By extrapolation, the drop in equilibrium position of the interface could be used to estimate approximately the solubility of the other liquid carbon dioxide. If there was no separation into two liquid phases, the miscibility was considered to be complete only after about three volumes of carbon dioxide were added for one of the other liquids.

In all cases with unmerged binodal curves a small circle is shown. This is the plait point or critical solution point, that is, the point at which the compositions of two liquid phases approach each other so that the interface fades out as a critical point. The position of the plait point can be of considerable importance. For example, compare Figures 39, 40 and 41. In Figure 39 the plait point is low, and the tie lines are so oriented that the cosolvent propane is much more soluble in the carbon dioxide layer than in the oil layer. This favors a good yield of oil since e is further from the left side, indicating a higher solubility than it would be otherwise. If propane were a polar compound, it would be unfavorable to quality of product because its selectivity would oppose that of carbon dioxide. but it is practically unselective and the selectivity of carbon dioxide contrlsl Vi. i li" IQ. l' l l .Inligure 4-1`the plait pointis -inthe middle and the tie lines-Aaresubstantially parallelto the side line..- The/cosolven't,ithiophene orl pyridine, is divided YYYalmost' equally between the `two layers; and y again the:l selectivity Aof carbon dioxide controls; AThe shallowness of the curve-is favorable in providing a. good yield'4 with thiophene or pyridine, which are good "homogenizers A In Figure`40', the plait point is close to the -left side andthe orientation of the tie 'lines indicates that'nitrobenze'ne dissolves in' the oi1 in preference to liquid carbon'dioxide. This 'results in a very low yield of oil dissolved in the carbon dioxideflayer. However, this orientation visr favorable to qualityof oil in the carbonwclioxide extract "since the opposite selectivity of nitrobenzene cooperates with that of liquid carbon dioxide; lIt has also ybeen found that a numberof solvents behave yas homogenizers for oils andliquid carbon dioxide. lIn the order of their effectivenessi. e., the amount of 'solvent required to homogenize oil and carbon dioxideg they are: pyridine; cyclohexanone; benzonitrile; thiox'ane; a picoline; -camphor; ,8' dichloroisopropyl ether; ethylphenyl acetate; thiophene; methyl, n-hexyl ketone; tolunitriles; acetal; acetyl chloride; anisole;.itertiarybutyl alcohol; n-butyl oxalate; crotonaldehyde;v ethyl benzoate; ethyl chlorocarbonate;4 ethylene bromide; ethyl formate; mesityl Ioxideyparalclehyde; propionaldehyde;v iso-propyl ether; valeraldehyde; benzene; n-butane; acroleinf-butyl Cellosolve vbutyraldehyde; chlOrObe'nZene;v chloroform; ethyl ether; ethyl salicylate; n-heptaldehyde'; methyl benzoate; n-butyraldehyde; acetophenone; benzaldehyde; 2-butanone"(methyl, ethyl ketone) ;"n-butane; .n-butylether; caproic acid; caprylic acid; carbon tetrachloride; dioxane; ethyl acetate; ethyl-carbonate; methylali! phenyl isocyanate; phosphorus trichl'o'ride; salicylaldehyde;` hydrogen` sulfide; limonene; methylacetate; o-chloro-" phenol; and methyl'salicylate. All "of the foregoing-solvents are better homogenizers than propanefln operation, a relatively small amount,

for'exampleli per cent, of pyridinel in the mixture or up to 34% `vof such homogenizers are used withliquid carbon dioxide.

Lcl'a'im:` 'l fw Y ivliv'lhe 'process of separating a hydrocarbon" mixture selected-from thegroup consisting of hydrocarbon mixturesranging from gas oils to lubricating oil stocks,into'fractions1at least 'one of which'has a higher viscosity index than that of the original mixture, which comprises: contacting -the mi-xture with liquid carbon dioxide anda solvent under suicient pressure to` maintaina carbon dioxide-rich phasein the liquid state, whereupon a raifinate phasel and an extract phase are formed, said solvent being at least partially miscible with liquid carbon dioxide and with the original mixture, and does not form threephases with the mixture and liquid carbon dioxide; effecting phase separation of the rafnate'and extract under said pressure; removing carbon' dioxide from' the extract phase; settling the'eXtract-'phase substantially free'of carbon dioxide, whereupon an extract-rafnate` and an extract-extract are formed; effecting phase separation ofthe -extract-raiiinate and the extractofhigher viscosity index than that of the original hydrocarbon mixture.

Cl s

` carbon dioxide-rich phase inthe liquid state,

whereupona raffinate phase and an extract phase arie formed, said solvent being miscible withliquid' `carbon dioxide and incompletely 'miscible with the originalmixturegfeifecting phase separation of the ranate and extract under said pressure;l removing carbon dioxidefrom the extract phase; settling the extract phase'substantially free of carbon dioxide,- whereupon van extract-raffinate and anextract-extract. are

` formed; eifecting phase separation of the extract-raffinate and the extract-extract; removing solvent fr`om=the extract-raflinate, thereby obtaining-a hydrocarbon fraction of higher viscosity index than that of the original hydrocarbon mixture. f, 3. The process of separatingA a lubricating oil into fractions vat least one of which has a? higher viscosity index than that of the original lubricat-` ingpil and lat least one of which `has a lower 1 viscosity index than that of the original oil, which comprises: vcontacting the oil with liquidfcarbon dioxide and a solvent under suificient'pressuret maintain a carbon ldioxide-rich phase' in the liquid state,- whereupon araifinate phase and an extract phase are formed; said solvent being miscible with'liquid carbon dioxideand incompletely miscible with the original oil; effecting phase separation of' the raffinate and extract under said pressure; removingV carbon dioxide I andsolvent 'from the raiiinate phase, thereby obtaining an oil fraction of lower 'viscosity index than'that ofthe original lubricating oil; removing'carbon dioxide from the extract phase; settling the extract phase substantially free of carbon dioxide,` whereupon anfextract-ranate and an extract-extract are formed; eifecting phase separation-of the extract-raihnate'and the extract-extract; removing solvent from the extractraffinate', thereby obtaining an yoil fraction of higher viscosity index than that of the original lubricating oil;v i

4. The continuous process of separating a lubricating oil into fractions at least one of which has ahigherfviscosity index thanf that of the original' oiland atleast one of which has a lower viscosity index than that of the original oil, which comprises:`v contacting the oil with liquid carbon dioxide 4and a solvent under Vsufficient pressure to'maintain a carbon fdioxide-rich phase in the liquidstateywhereupon a ralnate phase and-an extract'rphase vare formed, 'said solvent being miscible with liquid carbon dioxide and incompletely miscible with the original oil; .effecting phase separation'of the rafnate and extract under said pressure; removing carbon dioxide andsolvent from the rainate phase, thereby obandy solvent recoveredfrom said raffinate phase,

and removing from the system VVsaid oilfraction of lower viscosity index; removing carbon dioxide from` the extract'iphase; settling the extract phase substantially free of carbon dioxidegwhereupon an extract-rahinate and an extract-extract rare formed; eifecting phase separation of the extractrafnate and extract-extract; recycling to said contacting operation said extract-extract; removing solvent froin the extract-raffinate, therelby obtaining an oil fraction of higher viscosity index than that of the original lubricating oil; recycling to said contacting operation said solvent recovered from the extract-rariate; and removing from the system said oil of higher viscosity index.

5. The process as defined by claim 2 wherein the solvent is selected from the group consisting oi: Idjel-dichloiodiethyl ether, diethylene glycol monoethyl ether, isopropyl alcohol, B-ethoxyethanol, l-nitropropane, diacetone alcohol, ethyl lactate, ethyl oxalate, ethyl succinate, ethyl acetoacetate, ethyl chloroacetate, and benzonitrile.

6. The process as defined by claim 2 wherein the solvent is l-dichlorodiethyl ether.

7. The process as defined by claim 4 wherein the solvent is selected from the group consisting of: l6*61-diclilorodiethyl ether, diethylene glycol monoethyl ether, isopropyl alcohol, -ethoxyethanol, 1-nitropropane, diacetone alcohol, ethyl lactate, ethyl oxalate, ethyl succinate, ethyl acetoacetate, ethyl chloroacetate, and benzonitrile.

8. The process of separating a lubricating oil into fractions of different properties, which comprises: contacting the oil with liquid carbon dioxide and a solvent under sufficient pressure to maintain a carbon dioxide-rich phase in the liquid state, whereupon a rafnate phase and an extract phase are formed, said solvent being miscible with liquid carbon dioxide and incompletely miscible with the original oil; eiecting phase separation of the ranate and extract under said pressure; removing carbon dioxide from the extract phase; settling the extract phase substantially free of carbon dioxide, whereupon an extract-raffinate and extract-extract are formed; effecting phase separation of the extract-radinate and the extract-extract; removing solvent from the extract-rainate and the extract-extract, thereby obtaining fractions differing in properties and having diierent properties than those of the original mixture.

9. The process of separating a hydrocarbon mixture selected from the group consisting of hydrocarbon mixtures ranging from gas oils to lubricating oil stocks, into fractions at least one of which has a higher viscosity index than that of the original mixture, which comprises: contacting the mixture with liquid carbon dioxide and a solvent under sufficient pressure to maintain a carbon dioxide-rich phase in the liquid state, whereupon a raflinate phase and an extract phase are formed, said solvent being incompletely miscible with liquid carbon dioxide and with the original mixture, and does not form three phases with the mixture and liquid carbon dioxide; effecting phase separation of the rainate and extract under said pressure; removing carbon dioxide frorn the extract phase; settling the extract phase substantially free of carbon dioxide, whereupon an extract-raffinate and an extract-extract are formed; eiecting phase separation of the extract-raiiinate and extract-extract; removing solvent from the extract-rafinate, thereby obtaining a hydrocarbon fraction of higher viscosity index than that of the original hydrocarbon mixture.

10. The process of separating a lubricating oil into fractions at least one of which has a higher viscosity index than that of the original lubricat- 18 ing oil and at least one of which has a lower viscosity index than the original oil, which comprises: contacting the oil with liquid carbon dioxide and a solvent under suftlcient pressure to maintain a carbon dioxide-rich phase in the liquid state, whereupon a rainnate phase and an extract phase are formed, said solvent being incompletely miscible with liquid carbon dioxide and the original mixture, and does not form three phases with the oil and liquid carbon dioxide; effecting phase separation of the raffinate and extract under said pressure; removing carbon dioxide from the raffinate phase; settling the rainate phase substantially free of carbon dioxide, whereupon a raiinate-extract and a ranate-rafiinate aren formed; effecting'pha'se separation of the rainnate-extract and the rainate-rafiinate; removing solvent from the rafHnate-extract, thereby obtaining an oil of lower viscosity index than that of the original lubricating oil; removing carbon dioxide from the extract phase; settling the extract phase substantially free of carbon dioxide, whereupon an extract-rafiinate and an extractextract are formed; effecting phase separation of the extract-ramnate and the extract-extract; removing solvent from the extract-rattinate, thereby obtaining an oil Iraction of higher viscosity index than that of the original lubricating oil.

l1. The continuous process of separating a lubricating oil into fractions at least one of which has a higher viscosity index than that of the original oil and at least one of which has a lower viscosity index than that of the original oil, which comprises: contacting the oil with liquid carbon dioxlde and a solvent under suthcient pressure to maintain a carbon dioxide-rich phase in trie liquid state, whereupon a rainnate phase and an extract phase are formed, said solvent being incompietely miscible with liquid carbon dioxide and with the original oil, and does not form three phases with the oil and liquid carbon dioxide; enecting phase separation of said rattlnate and extract under said pressure; removing carbon dioxide from the raffinate phase; settling the raliinate phase substantiaily free of carbon dioxide, whereupon a rainnate-extract and a. raffinate-rathnate are formed; recycling to said contacting operation said raffinate-rattinate; removing solvent from the raffinate-extract, thereby obtaining an oil of lower viscosity index than that of the original lubricating oil; recycling to said contacting operation liquid carbon dioxide and solvent recovered from said raffinate-raffinate and raffinate-extract, respectively; removing from the system said oil fraction of lower viscosity index; removing carbon dioxide from the extract phase; settling the extract phase substantially free of carbon dioxide, whereupon an extract-raffinate and an extractextract are formed; eiecting phase separation of the extract-railinate and the extract-extract; recycling to said contacting operation said extractextract; removing solvent from the extract-raffinate, thereby obtaining an oil fraction of higher viscosity index than that of the original lubricating oil; recycling to said contacting operation said solvent recovered from the extract-rafnate; and removing from the system said oil of higher viscosity index.

12. The process as defined by claim 9 wherein the solvent is selected from the group consisting of: aniline, o-cresol, p-cresol, o-toluidine, methylaniline, o-chloroaniline, -hydroxyethyl acetate, tetrahydrofurfuryl alcohol, phenylethanol, pinacol, phenol, phenylacetonitrile, hydrocinnamaldehyde, methyl phthalate, o-nitrochlorobenzene,

19 triethylene glycol, o-nitrobiphenyl, o-anisidine, benz'oic anhydride, cinnamaldehyde, benzyl alcohol, and ethyl phthalate.

13. The process as deiined by claim 9 wherein the solvent is aniline.

14. The process as dened by claim 9 wherein the solvent is tetrahydrofurfuryl alcohol.

15. The process as defined by claim 11 wherein the solvent is selected from the group consisting of aniline, o-cresol, p-cresol, o-toluidine, methylanilihe, o-chloroaniline, tetrahydrofurfuryl alcohol, phenylethanol, pinacol, phenol, phenylacetonitrile, hydrocinnamaldehyde, methyl phthalate, o-nitrochlorbenzene, o-nitrobiphenyl, o-anisidine, benzoic anhydride, cinnamaldehyde, benzyl alcohol, and ethyl phthalate.

16. The process of separating a mixture of compounds selected from the group consisting of hydrocarbon mixtures ranging from gas oils to lubricating oil stocks, into fractions of different properties, which comprises: contacting the mixture with liquid carbon dioxide and a solvent un- 'der sufficient pressure to maintain a, carbon dioxide-rich phase in the liquid state, whereupon a raflinate phase and an extract phase are formed, said solvent being incompletely miscible with liquid carbon dioxide and with the original mixture of compounds, and does not form three phases with the original mixture of compounds and liquid carbon dioxide; effecting phase separation of the raffinate and extract under said pressure; removing carbon dioxide from the raiiinate phase; settling the raflinate phase substantially free from carbon dioxide, whereupon e, rainate-extract and a rafnate-rainate are formed; removing solvent from the rainate-rafnate and raffinateextract, thereby obtaining fractions differing in properties and having different properties from 'those of the original mixture; removing carbon dioxide from the extract phase; settling the extract phase substantially free from carbon dioxide, whereupon an extract-rainate and an extract-extract are formed; effecting phase separation of the extract-raffinate and the extract-extract; removing solvent from the extract-rafnate and the extract-extract, thereby obtaining fractions differing in properties and having diierent properties from those of the original mixture and the fractions recovered from the rainate-raiinate andthe rafnate-extract.

17. The process of separating a lubricating `oil into fractions of different properties, which comprises: contacting the oil with liquid carbon di- 'oxide and a solvent lunder suicient pressure to maintain a carbon dioxide-rich phase in the liquid state, whereupon a raffinate phase and an extract phase are formed, said solvent being incompletely miscible with liquid carbon ldioxide and with the original oil, and does not form three phases with the original oil and liquid carbon dioxide; effecting phase separation of the rafnate and extract phases under said pressure; removing carbon dioxide from the extract phase; settling the extract phase substantially free of carbon dioxide, whereupon an extract-raihate and an extractextract are formed; eiecting phase separation of the extract-rafnate and the extract-extract; removing solvent from the extract-ralinate and the extract-extract, thereby obtaining oil fractions diiering in properties and having different properties than those of the original lubricating oil.

` 18. The process of separating a polycyclic hydrocarbon and a monocyclic hydrocarbon from a mixture containing the same, which comprises: contacting the mixture with liquid carbon dioxide and a solvent under suicient pressure to maintain a carbon dioxide-rich phase in the liquid state, whereupon a rainate phase and an extract phase are formed, said solvent being miscible with liquid carbon dioxide and incompletely miscible with the original mixture; eiecting phase separation of the extract and rainate un` der said pressure; removing carbon dioxide from lthe extract phase; settling the extract phase substantially free of carbon dioxide, whereupon an extract-raflinate and an extract-extract are formed; effecting phase separation of the extractrainate and the extract-extract; removing solvent from the extract-raiiinate, thereby obtaining a fraction substantially richer in said monocyclic hydrocarbon than the original mixture; removing solvent and lcarbon dioxide from the raffinate phase, thereby obtaining a fraction substantially richer in said polycyclic hydrocarbon than the original mixture.

19. The process of separating a polycyclic hydrocarbon and a monocyclic hydrocarbon from a mixture containing the same, which comprises: lcontacting the mixture with liquid carbon dioxide and a solvent under sufiicient pressure to maintain a carbon dioxide-rich phase in the liquid state, whereupon a raffinate phase and an extract phase are formed, said solvent being incompletely miscible with liquid carbon dioxide and with the original mixture, and does not form three phases with the original mixture and liquid carbon dioxide; effecting phase separation of the rainate and extract under said pressure; removing carbon dioxide from the extract phase; settling the extract phase substantially Yfree of carbon dioxide, whereupon an extract-raffinate and an extractextract are formed; eiecting phase separation of the extract-raffinate and extract-extract; removing solvent from the extract-rafnate, thereby obtaining a fraction substantially richer in said monocyclic hydrocarbon than said original mixture; removing carbon dioxide from the railinate phase; settling the raffinate phase substantially free of Vcarbon dioxide, whereupon a ramnateextract and a ranate-rainate are formed; effecting phase separation of the ra'iiinate-extract and the rafnate-ranate; removing solvent from the ramnate-extract, thereby obtaining a fraction substantially Vricher in said polycyclic hydrocarbon than said original mixture.

ALFRED W. FRANCIS.

REFERENCES "CITED The following references 'are of record in the rile of this patent:

UNITED STATES PATENTS Number Name Date 2,034,495 Sullivan, Jr Mar. 17, 1936 2,130,147 Milmore V Sept. 13, 1938 2,188,051 Lantz 1-- Jan. l23, 1940 2,246,227 Webb r June 17, 1941 2,346,639 `Andrews Apr. 18, 1944 Kalichevsky, Modern Methods of Reiining Lubricating Oils, (1938). 

1. THE PROCESS OF SEPARATING A HYDROCARBON MIXTURE SELECTED FROM GROUP CONSISTING OF HYDROCARBON MIXTURES RANGING FROM GAS OILS TO LUBRICATING OIL STOCKS, INTO FRACTIONS AT LEAST ONE OF WHICH HAS A HIGHER VISCOSITY INDEX THAN THAT OF THE ORIGINAL MIXTURE, WHICH COMPRISES: CONTACTING THE MIXTURE WITH LIQUID CARBON DIOXIDE AND A SOLVENT UNDER SUFFICIENT PRESSURE TO MAINTAIN A CARBON DIOXIDE-RICH PHASE AND AN EXSTATE, WHEREUPON A RAFFINATE PHASE AND AN EXTRACT PHASE ARE FORMED, SAID SOLVENT BEING AT LEAST PARTIALLY MISCIBLE WITH LIQUID CARBON DIOXIDE AND WITH THE ORIGINAL MIXTURE, AND DOES NOT FORM THREE PHASES WITH THE MIXTURE AND LIQUID CARBON DIOXIDE EFFECTING PHASE SEPARATING OF THE ROFFINATE AND EXTRACT UNDER SAID PRESSURE; REMOVING CARBON DIOXIDE FROM THE EXTRACT PHASE; SETTLING THE EXTRACT PHASE SUBSTANTIALLY FREE OF CARBON DIOXIDE, WHEREUPON AN EXTRACT-RAFFINATE AND AN EXTRACT-EXTRACT ARE FORMED; EFFECTING PHASE SEPARATION OF THE EXTRACT-RAFFINAATE AND THE EXTRACTEXTRACT; REMOVING SOLVENT FROM THE EXTRACT-RAFFINATE, THEREBY OBTAINING A HYDROCARBON FRACTION OF HIGHER VISCOSITY INDEX THAN THAT OF THE ORIGINAL HYDROCARBON MIXTURE. 